The background is described with respect to LTE (Long Term Evolution). The skilled person will however realize that the principles of the invention may be applied in other radio communication systems, particularly in communication systems that rely on scheduled data transmissions.
The downlink transmission of the LTE (Long Term Evolution), or E-UTRAN radio access, is based on Orthogonal Frequency Division Multiplex (OFDM). The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 1, where each resource element (RE) corresponds to one OFDM subcarrier during one OFDM symbol interval. The dark shadowed resource elements form a resource block.
In the time domain, transmissions in LTE are structured into frames and subframes. Each frame of length Tf=10 ms consists of ten equally-sized subframes of length Tsubframe=1 ms. Each subframe, in turn, consists of two equally-sized slots of length Tslot=0.5 ms.
Resource blocks (RBs) are also defined in LTE, where each RB consists of 12 contiguous subcarriers during one slot. The subcarrier spacing is set to Δf=15 kHz. In addition, a reduced subcarrier spacing of 7.5 kHz is defined targeting multicast broadcast transmissions in single-frequency networks.
Generally a resource element may be defined by certain ranges in any combination of the transmission resource, which are essentially time, frequency, code and space, depending on the actual transmission system under consideration.
The LTE time domain structure, in which one radio frame is divided into the 10 subframes #0 to #9 and each subframe is divided into a first and a second slot, wherein the first slot is an early part and the second slot is a later part of each subframe, is depicted in FIG. 2.
In LTE data transmissions to/from a user equipment (UE) are under strict control of the scheduler located in the eNB. Control signaling is sent from the scheduler to the UE to inform the UE about the scheduling decisions. This control signaling, consisting of one or several PDCCHs (Physical Downlink Control Channels) as well as other control channels, is transmitted at the beginning of each subframe in LTE, using 1-3 OFDM symbols out of the 14 available in a subframe (for normal CP and bandwidths larger than 1.8 MHz, for other configurations the numbers may be different).
Downlink scheduling assignments, used to indicate to a UE that it should receive data from the eNB occur in the same subframe as the data itself. Uplink scheduling grants, used to inform the UE that it should transmit in the uplink occur a couple of subframes prior to the actual uplink transmission.
Generally, control data may comprise at least one of a downlink assignment and an uplink grant.
Among other information necessary for the data transmission, the scheduling assignments (and grants) contain information about the frequency-domain location of the resource blocks used for data transmission in the first slot. The frequency-domain location of the RBs in the second slot is derived from the location in the first slot, e.g. by using the same frequency location in both slots. Thus, scheduling assignments/grants operate on pairs of resource block in the time domain. An example hereof is shown in FIG. 3.
In FIG. 3, the slopingly hatched parts in each resource block 0 to 9 contains control data, whereas the horizontally hatched parts contain payload data. The subframe is divided into a first slot and a second slot. The control data is part of the first slot.
Relaying is considered for LTE-Advanced as a tool to improve e.g. the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas. The relay node (RN) is wirelessly connected to the radio-access network, for example via a donor cell controlled by a donor eNodeB (eNB). The RN transmits data to/from UEs controlled by the RN and may use the same air interface as an eNB, i.e. from a UE perspective there is no difference between cells controlled by a RN and an eNB.
Due to the relay transmitter causing interference to its own receiver, simultaneous eNB-to-RN and RN-to-UE transmissions on the same frequency resource may not be feasible unless sufficient isolation of the outgoing and incoming signals is provided e.g. by means of specific, well separated and well isolated antenna structures. Similarly, at the relay it may not be possible to receive UE transmissions simultaneously with the relay transmitting to the eNB.
One possibility to handle the interference problem is to operate the relay such that the relay is not transmitting to terminals when it is supposed to receive data from a control node, e.g. the donor eNodeB, i.e. to create “gaps” in the relay-to-UE transmission. These “gaps” during which terminals (including 3GPP Rel-8 terminals) are not supposed to expect any relay transmission can be created by configuring MBSFN subframes as exemplified in FIG. 4. MBSFN subframes contain a small control signaling part at the beginning, followed by a silent period where the UEs do not expect any transmissions from the RN.
During the time period or frame or subframe, in which the UE does not expect data and/or in which the RN does not transmit data to the UEs, the RN can receive data, for example control data of the eNB.
RN-to-eNB transmissions can be facilitated through scheduling by not allowing any terminal-to-relay transmissions in some subframes.
One aim of the invention is to provide methods for efficiently transferring control data and payload data in a network scenario comprising a control node (donor eNB), a relay node and possibly several UEs. Therein the above interference problem associated with the use of relay nodes shall be solved.
The invention is particularly relevant for LTE based systems. Downlink control signaling is discussed in Section 16.2.4, pages 333 to 336, of the book entitled 3G Evolution: HSPA and LTE for Mobile Broadband, first edition 2007 by Dahlmann, Parkvall Skoeld and Beming. It is also pointed to the standards 3GPP LTE Rel-10 and to the technical reports 3GPP TR 36.814 and 36.912. Multiplexing a Relay Physical Downlink Control Channel (R-PDCC) in the downlink subframe from the donor eNB is discussed in U.S. 61/308,385. The cited references/documents are incorporated by reference herewith.